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+4 votes

In P-persistent CSMA network there are 5 systems in a slot. The probability of station not transmitting the data is 0.6. Only two stations should transmit the data to avoid collision. What is the probability that channel is collision free?

My answer is 0.6825 and answer given is 0.34 - 0.35.

I solved this as P (no collision) = either 2 stations are transmitting or 1 station or none.

in Computer Networks by Boss (13.6k points)
edited by | 1.2k views

2 Answers

+3 votes
Best answer
Favorable case here is no station is transmitting, exactly one is transmitting or exactly 2 is transmitting.

$P = {}^5C_0 \times {0.6}^5 + {}^5C_1 \times {0.6}^4{0.4} + {}^5C_2 \times {0.6}^3{0.4}^2
\\= 0.68256.$
by Veteran (431k points)
selected by
Is this ans correct or 0.365 if we will take on 5C2 case???

Can u clarify?
+8 votes

In question ask only two stations transmit. So, we consider two stations only.

probability =5C2(0.42)(0.63)=0.3456

by (91 points)
but of only one statuon transmit then also it will be collisoin free. why we are not considering that case?
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